A multi-column element establishes a new block formatting context, as per CSS 2.1 section 9.4.1. However, the top margin of the first element and the bottom margin of the last element collapse with the margins of the multi-column element as per the normal rules for collapsing.

He says that the margins should not collapse through the multicol element

06:42:51 [fantasai]

Sylvain: Alex was concerned about this, too.

06:43:22 [fantasai]

fantasai explains that this behavior was put there because in the past there was no value-based distinction between a multicol element with one column and a normal element, and we didn't want to introduce a discontinuity there

06:43:52 [fantasai]

but since there's now a default auto value for column-count instead of 1, this problem doesn't exist